Hidden Upgrade

Matt Tomkins fits a taller differential for fast-road touring.

Swap your differential for more comfortable cruising.

Why did you fit it?

This Minor is used regularly for motorway runs and, with a standard 4.22:1 differential fitted, keeping pace with modern traffic means the engine is revving higher than I’d like. The 3.9:1 ratio differential from an MG Midget is a straight swap for the 4.22:1 Minor unit, so is a sensible upgrade for any Minor that is used for long distances.

What is the hardest part?

Not encountered in this case is the possibility of an axle casing designed for the 4.55:1 ratio A-series differential (fitted to 948cc Minors) that relies on a bung in the aluminium differential housing for oil filling. If a later 4.22:1, 3.9:1 or

3.7:1 differential is to be fitted, either a filler plug needs drilling and a boss welding in place, or filling should be carried out by means of a pre-measured amount of axle oil introduced through either the breather hole on top of the axle casing or through the end of the axle casing with one side of the car raised and that side’s half shaft not yet fitted.

What’s the choice?

The majority of Morris Minors, with their 14in wheels, were fitted with either

4.55:1 (948cc cars) or 4.22:1 (1098cc cars) differentials. The sporty MG Midget with it’s 13 inch wheels was fitted with a 3.9:1 and later with a 3.7:1 ratio. Wolseley 1500s and Riley 1.5s, with their more powerful B-series engines, could pull a 3.7:1 differential away from the lights even with their 14in wheels.

Remanufactured crownwheels and pinions in both 3.9:1 and 3.7:1 ratios are available outright from MGOC Spares if you cannot source a good secondhand unit.